Overall Research Strategy: Summary/Abstract Pancreatitis is a potentially fatal disease with significant morbidity and mortality the pathogenesis of which remains obscure. Specific therapies to prevent pancreatitis or reduce injury are lacking. The proposed Program focuses on disorders of key orgenells in the pancreatic acinar cell as a central pathogenic mechanism initiating and driving pancreatitis. The physiologic function of the acinar cell is to synthesize, transport, store, and secrete digestive enzymes. These functions rely on the actions of endoplasmic reticulum (ER), the endo- lysosomal system and autophagy to coordinate protein synthesis, processing, trafficking and degradation. Based on our published and preliminary studies, we propose the following novel hypothesis: dysfunction of acinar cell organellar machinery that mediates protein processing, trafficking, and degradation initiates and promotes the cellular pathology of pancreatitis. We propose four Projects that use multidisciplinary approaches to study the following in the context of acute pancreatitis: The role of key regulators of protein trafficking, Rab GTPases, in endosomal and lysosomal/autophagic dysfunction in pancreatitis (Project 1); The role of regulatory proteins D52, Rab5 and AP3 in inhibition of secretion and intracellular zymogen activation (Project 2); The roles of the multifunctional scaffold protein p62/SQSTM1 and impaired autophagy in the pathogenesis of pancreatitis (Project 3); The role of ER stress responses, and particularly the ER stress regulator sXBP1, in defective endosomal function, autophagy, and secretion inhibition (Project 4). The Projects use three supporting Cores which will perform standardized animal models of pancreatitis on wild-type and genetically modified mice, generate new mouse lines, provide histopathologic evaluation of human pancreatic tissue, isolation of human acinar cells, viral transduction of both mouse and human acinar cells, and Web-based resource repository and data sharing system. Thus, the Program will elucidate novel pathogenic mechanisms of pancreatitis resulting from disorders of key acinar cell organelles; identify new molecular targets and promote the development of new therapeutic approaches for disease treatment; integrate and catalyze the work of investigators with various areas of expertise to define the mechanism of pancreatitis.